the needles entering the downpipe will get lodged in any of 4 - 45 deg elbows
I have lots of mature trees near me (including field maples which have very large leaves) and in one area the offset would clog regularly, causing the gutter to overflow the next time it rained.
I removed the offset and put in a downpipe from the outlet to a hopper. In the bottom of the hopper I put a piece of steel mesh to catch the leaves, etc, that get in there. Obviously the hopper now needs cleaning but it is much lower - so I can use a step ladder rather than an extension ladder - and it brings most of the muck to one place.
but at around £110 each, I need 14 of them so at £1540
Before I removed that offset I looked at adding a leaf catcher and I found they varied greatly in price. I can't find the list of options I looked at but with a quick web search I found
Reducing any build-up in your guttering, our Downpipe Leaf Separator is designed to look after your guttering and reduce the risk of blockages in drains.
www.directwatertanks.co.uk
Fit the Leaf Catcher on the downpipe at a convenient height. Don’t stand on ladders to unblock gutters! This leaf guard fits round & square downpipes
www.celticsustainables.co.uk
all cheaper than that.
Also, the house may have 14 downpipes but that does not necessarily mean that all 14 need work. The side nearest the trees will probably catch the majority of the debris.
If the bulk of the debris can be brought down to low level (accessible from the ground) and removed then the gutters may still need to be cleaned, but how often this needs to be done or how long it takes may well be reduced.
It probably would not help anyway, if it's your gutters becoming obstructed.
The gutters only get blocked because the debris stays there, if it was washed down as suggested in post #3 then a catcher may well work.
I found perforated gutter covers which would work albeit very expensive, but again all these would do is provide a platform for the needles to collect
I put in a load of those gutter covers and subsequently removed them. I think that if you have a small to moderate amount of leaves they stop the leaves from going into the gutters and then the leaves will dry and blow off.
However if you have a lot of leaves, more will land before the first ones have dried, eventually forming a continuous mat which will catch all subsequent leaves and cause the gutter to overflow.
The problem is that I have a lot of Pine trees in my garden which are under a council preservation order so I can't get them felled.
A TPO may well stop you from felling the trees but it does not necessarily stop them from being cut back.
There is a very large TPO here and we have a copper beech that is over 150yo. The flats next door were built far to close and so their gutters used to regularly fill with beech mast. They got permission from the council to cut back the one branch that was actually overhanging the flats which, AFAIUI, fixed the problem.
So you may be able to reduce the problem by cutting back the branches nearest to the house.